<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>选择器</title>
    <script src="js/jquery-3.2.1.js"></script>
</head>
<body>
    <div class="parent">
      <div class="child">
          hello world
      </div>
    </div>
    <script>
        let arr = $(".parent .child");
        console.log(arr);
    </script>
</body>
</html>